The present invention is directed to polymer resin/dispersed modifier compositions and methods for producing polymer resin/dispersed modifier compositions. Particularly, the present invention is directed to improved polyethylene oxide/dispersed modifier compositions, methods for improving the melt processability of polyethylene oxide/dispersed modifier compositions, and thermoformable articles formed from the polyethylene oxide/dispersed modifier compositions.
Disposable personal care products such as pantiliners, diapers, tampons etc. are a great convenience. Such products provide the benefit of one time, sanitary use and are convenient because they are quick and easy to use. However, disposal of such products is a concern due to limited landfill space. Incineration of such products is not desirable because of increasing concerns about air quality and the costs and difficulty associated with separating such products from other disposed, non-incineratable articles. Consequently, there is a need for disposable products which may be quickly and conveniently disposed of without dumping or incineration.
It has been proposed to dispose of such products in municipal and private sewage systems. Ideally, such products would be flushable and degradable in conventional sewage systems. Products suited for disposal in sewage systems and that can be flushed down conventional toilets are termed xe2x80x9cflushablexe2x80x9d. Disposal by flushing provides the additional benefit of providing a simple, convenient and sanitary means of disposal. Personal care products must have sufficient strength under the environmental conditions in which they will be used and be able to withstand the elevated temperature and humidity conditions encountered during use and storage yet still lose integrity upon contact with water in the toilet. Therefore, a water-disintegratable material having mechanical integrity when dry is desirable.
Due to its unique interaction with water and body fluids, polyethylene oxide (hereinafter PEO) has been considered as a component material for water-disintegratable films, fibers, and flushable products as disclosed in U.S. patent applications Ser. Nos. 09/001,831; 09/001,408; 09/001,525; and 09/219,198; and U.S. Pat. No. 6,117,947; all of which are assigned to Kimberly Clark Worldwide, Inc. PEO,
xe2x80x94(CH2CH2O)nxe2x80x94, 
is a commercially available water-soluble polymer that can be produced from the ring opening polymerization of ethylene oxide, 
Because of its water-soluble properties, PEO is desirable for flushable applications. However, there is a dilemma in melt processing PEO. Low molecular weight PEO resins have adequate melt properties for limited melt processing, but have limited solid state properties when melt processed into structural articles such as films.
An example of a low molecular weight PEO resin is POLYOX(copyright) WSR N-80 PEO, which is commercially available from Union Carbide. POLYOX(copyright) WSR N-80 PEO has an approximate molecular weight of 200,000 g/mol as determined by Theological measurements. As used herein, xe2x80x9clow molecular weight PEO compositionsxe2x80x9d are defined as PEO compositions with an approximate molecular weight of less than and including about 300,000 g/mol.
In the personal care product industry, flushable thin-gauged films and melt-spun fibers are desired for commercial viability and ease of disposal. The low melt strength and low melt elasticity of low molecular weight PEO prevent low molecular weight PEO to be drawn into films having a thickness of less than about 1.0 mil. Efforts have been attempted to improve the processability of PEO by blending the PEO with a second polymer, for example, an elastomeric polymer such as ethylene-vinyl acetate copolymer, to produce a water-shrinkable film. See, for example, U.S. Pat. Nos. 5,641,562, assigned to Kimberly-Clark Worldwide, Inc. The PEO/ethylene-vinyl acetate copolymer composition is able to be processed into films of about 1.2 mils in thickness. However, the composition and resulting film are not water-soluble, especially at high levels of ethylene-vinyl acetate copolymer, i.e. about 30 weight percent.
More importantly, thin films made from low molecular weight PEO are too weak and brittle to be useful for personal care applications. Low molecular weight PEO films have low tensile strength, low ductility, and are too brittle for commercial use. Further, films produced from low molecular weight PEOs become brittle during storage at ambient conditions. Such films shatter and are not suited for commercial applications.
High molecular weight PEO resins produce films with improved mechanical properties compared to films produced from low molecular weight PEO resins. An example of a high molecular weight PEO is POLYOX(copyright) WSR 12K PEO, which is commercially available from Union Carbide. POLYOX(copyright) WSR 12K PEO has a reported approximate molecular weight of 1,000,000 g/mol as determined by rheological measurements. As used herein, xe2x80x9chigh molecular weight PEOsxe2x80x9d are defined as PEOs with an approximate molecular weight of greater than and including about 400,000 g/mol.
However, high molecular weight PEOs have poor processability due to their high melt viscosities and poor melt drawabilities. Melt pressure and melt temperature during melt processing are significantly elevated during melt extrusion of high molecular weight PEOs. During extrusion of high molecular weight PEOs, severe melt fracture is observed. Only very thick sheets can be made from high molecular weight PEOs. High molecular weight PEOs cannot be thermally processed into films of less than about 3-4 mil in thickness. High molecular weight PEOs suffer from severe melt degradation during extrusion and melt processing. This results in breakdown of the PEO molecules and formation of bubbles in the extrudate, as well as, irritating vapors from the degradation of the PEO. The inherent deficiencies of high molecular weight PEOs make it impossible to utilize high molecular weight PEOs in film applications. Even the addition of high levels of plasticizer to the high molecular weight PEOs do not improve the melt processabilities sufficiently to allow the production of thin films without melt fracture and film breakage occurring. In addition, the use of plasticizer in films causes latent problems due to migration of the plasticizer to the film surface. Thus, currently available PEO resins are not practical for melt processing into thin films for personal care applications.
U.S. patent application Ser. No. 09/113,448 discloses a blend comprising PEO and latex which has improved physical properties such as reduced modulus and increased elongation. The blend creates a new physical structure. But the PEO was modified by a chemical reaction and therefore the PEO still retains its own physical properties. However, what is still needed is a chemically modified PEO and modified elastomer structure with improved melt processability in making thin films or fibers and improved physical and mechanical properties.
What is needed in the art is a PEO composition that overcomes the difficulties of melt processing and provides a commercially feasible product for use in flushable, personal care applications.
The present invention is directed to compositions having improved melt processability and improved mechanical characteristics, such as improved ductility, toughness and tear resistance. The compositions of the present invention comprise a polymer resin component, a dispersed modifier component derived from an emulsion, and a monomer grafted onto one or both of the polymer resin component and the modifier component. In one embodiment, the polymer resin comprises PEO. The present invention is further directed to grafted polymer resin/dispersed modifier compositions having improved processability, and methods for producing the same. Particularly, the present invention is directed to polymer blend compositions made by a melt extrusion process, which contain PEO and a dispersed modifier, which may be further chemically modified by grafting one or more vinyl monomers to the PEO and/or the dispersed modifier during a reactive extrusion process.
The present invention is also directed to films, fibers, and other thermoformable articles made from the melt processable compositions. More particularly, the present invention relates to compositions comprising PEO/modifier compositions and methods of modifying PEO/modifier compositions to improve their melt processability by grafting polar vinyl monomers, such as poly(ethylene glycol) methacrylates of different molecular weights, or 2-hydroxyethyl methacrylate, onto one or both of the PEO and modifier components of the composition. The grafting step is accomplished by melt blending a PEO, a modifier, a polar vinyl monomer(s) and an initiator, and applying heat and intensive shear. In one embodiment, the method of modification is a reactive-extrusion process. PEO compositions modified in accordance with the present invention have improved melt processability and may be thermally processed into films, fibers, and other articles, which have improved physical and mechanical properties over films, fibers, and articles similarly processed from unmodified PEO compositions, and grafted PEO compositions.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments.